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mike49504 9th November 2008 07:54 PM

i checked the other njm2068l's in the amp pin 8 of all the njm2068's have no reading on them and all of then on pin 4 is very low readings my next thought mabye the kia494l is bad could that be a possibaly ive checked pretty much everything else and it tests fine

Perry Babin 9th November 2008 07:58 PM

If the amp is producing rail voltage, the 494 is OK.

Do you have positive AND negative rail voltage?

Are they they same above/below ground?

mike49504 9th November 2008 08:12 PM

the readings from the kia494l are


Perry Babin 9th November 2008 08:35 PM

You have the pin configuration wrong.

From what I can tell, the IC is working but has been shut down for some reason. You missed one pin.

mike49504 10th November 2008 11:56 AM

i hooked the amp up to power to test somemore and 2 more caps blew and a bd911 also went so now the amp powers up with the protect light on but now the voltage on the pads of the 47uf 16v cap reads about 2 volts now wondering if maybe the bd911 was bad all along it was reading fine but when it blew all the readings on the pads for the caps measure fine now

mike49504 14th December 2008 12:14 AM

im back to working on this again. i pulled the reflectors and power it up and the problem is in the power supply. the problem im having if the amp will idle fine for about 5 secs the it starts pulling 40 amps of current. wondering what might cause this

jol50 14th December 2008 04:50 AM

Bad transformer?

Perry Babin 14th December 2008 05:28 AM

A shorted transformer could be causing this. Since it was producing rail voltage earlier, the short would likely be intermittent. With an inline current limiter in the B+ line, twist/push/pull on the transformers to see if the short opens. Connect the scope to the tab of the power supply FETs to see if/when it goes from a flat line to a square wave.

It's also possible that you have a defective driver for the power supply FETs. If the driver isn't pulling the gate voltage back to ground, it would cause excessive current draw. If you look at the gate signal for the power supply FETs, you should see the voltage drop back to ground quickly on the falling edge of the waveform. Since it's drawing excessive current, you'll have to use a current limiter when viewing the waveforms.

mike49504 14th December 2008 07:28 AM

WOW!!! How lucky can i be. Now i have 3 amps with transformer problems. i can see where the transformer is shorted and it also has a loose winding. is there anyway to coat the shorted lead. its bare only about a half inch. also i have to pick up on the transformer to get the amp to turn on. Anyway of fixing theese 2 problems without rewinding it

Also when i recieved the amp for the outputs they had 2sc5359's in it and someone told me that 2sc5200's belong there doesa anyone know Im wondering because 1's a pnp and the other is npn

any help would greatly appericated

Perry Babin 14th December 2008 07:57 AM

Many times, the bare area is near the end of the shorted winding and you can use heatshrink tubing to insulate it.

If the windings are loose, you can coat a piece of paper with epoxy and insert it between the windings. Get the paper just about where you want it before you apply the epoxy.

If the windings are tight but the short is near the end of the winding, you can possibly pull a string between the windings and epoxy it in place. I use 80lb braided Dacron fishing line. I mainly use this as a preventative measure on inductors that are known to have a VERY high failure rate but it also works after the windings have shorted.

If the winding is shorted where the terminal winding turns down toward the board, you may be able to insert a piece of heavy cardboard between the terminal winding and the rest of the windings. Apply a good adhesive like E6000 or Goop to the cardboard before inserting it. I wouldn't use epoxy there because you may have to solder the terminal and the fumes from burning epoxy are VERY unpleasant.

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